This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ACK acknowledgment
ARQ automatic repeat request
CA carrier aggregation
CIF carrier indicator field
CC component carrier
DCI downlink control information
DL downlink (eNB to UE)
eNB EUTRAN Node B (evolved Node B/base station)
E-ARFCN E-UTRA absolute radio frequency channel number
EPC evolved packet core
E-UTRAN evolved UTRAN (LTE)
HARQ hybrid ARQ
IMT international mobile telecommunications
ITU-R international telecommunication union-radio
LTE long term evolution
MM/MME mobility management/mobility management entity
MIMO multiple input multiple output
MU multi-user
NACK negative ACK
OFDMA orthogonal frequency multiple division access
PC power control
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PUSCH physical uplink shared channel
RACH random access channel
RRC radio resource control
SC-FDMA single carrier, frequency division multiple access
TA time alignment
UE user equipment
UL uplink (UE to eNB)
UTRAN universal terrestrial radio access network
In the communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE, E-UTRA or 3.9G), the LTE Release 8 is completed, the LTE Release 9 is being standardized, and the LTE Release 10 is currently under development within the 3GPP. In LTE the downlink access technique is OFDMA, and the uplink access technique is SC-FDMA, and these access techniques are expected to continue in LTE Release 10.
FIG. 1A reproduces FIG. 4-1 of 3GPP TS 36.300, V8.6.0 (2008-09), and shows the overall architecture of the E-UTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME and to a Serving Gateway. The S1 interface supports a many to many relationship between MMES/Serving Gateways and the eNBs.
Of particular interest herein are the further releases of 3GPP LTE targeted towards future IMT-Advanced systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). LTE-A is directed toward extending and optimizing the 3GPP LTE Release 8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Release 10. LTE-A is expected to use a mix of local area and wide area optimization techniques to fulfill the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Release 8. Topics that are included within the ongoing study item include bandwidth extensions beyond 20 MHz, among others.
The bandwidth extension beyond 20 MHz in LTE-Advanced (for example, beyond 20 MHz but aggregations of larger or smaller component carriers is to be done via carrier aggregation (CA), in which several Release 8 compatible carriers are aggregated together to form a system bandwidth. This is shown by example at FIG. 1B in which there are 5 Release 8 compatible CCs aggregated to form one larger LTE-Advanced bandwidth. The purpose for aggregating individual e.g. 20 MHz Release 8 compatible component carriers (CCs) is that each existing Release 8 terminal can receive and/or transmit on one of the CCs, whereas future LTE-Advanced terminals could potentially receive/transmit on multiple CCs at the same time, thus having support for large bandwidth. FIG. 1B is specific to LTE-Advanced but makes clear the general concept of CA regardless of what size the CCs; for example smaller frequency chunks such as 10 MHz CCs can be aggregated to get a 20 MHz bandwidth and CCs can be made larger than 20 MHz. LTE Release 8 allows bandwidths of 1.4 MHz, 5 MHz and 10 MHz as well as 20 MHz, so any of these may be the size of a CC.
In LTE Release 8, the PDCCH could only be used to indicate a PDSCH/PUSCH sent on its own DL CC or its paired UL CC. For Release 10 UEs there is the possibility that the eNB and the UE can use more than one cell for communication on more than one frequency band (more than one CC). In order to facilitate this functionality there is a need to find solutions to how to potentially activate and deactivate usage of CA.
There is already specified the concept of cross CC scheduling, so that an allocation (for example on a PDCCH) sent by the eNB on one CC (cell) can schedule/allocate radio resources on a different CC (cell). In this cross CC scheduling grant there is a 3 bit Carrier Indication Field (CIF), added to the DCI format, which indicates on which CC the allocated resources lie. The PDCCH is sent on a per cell basis, so where there are multiple CCs the PDCCH is described as being sent on a cell of a specific CC. It is undecided if the CIF meaning can be different for UL and DL.
It is considered also that the Release 10 UEs may not necessarily be scheduled across the entire five CCs shown by example at FIG. 1B (or however many total CCs there are in the whole bandwidth), but rather there is a subset of them for which the UE is configured, via RRC signaling. This avoids the UE having to blind detect on every possible CC in the whole bandwidth to find its PDCCH, a power intensive operation. From the UE's configured set of CCs (which it the UE's CA), there must then be a more dynamic way than RRC signaling to coordinate between the eNB and the UE exactly which CCs are active, and so a mechanism to activate and de-activate cells/individual CCs which belong to the UE's configured CC set. RRC signaling is not considered effective for this purpose because its semi-static nature would impose too much delay especially given inherent delays and time uncertainty introduced due to HARQ and ARQ when activating and/or de-activating any CC.
Relevant proposals in this regard have been presented to 3GPP, including: R2-096502 (3GPP TSG-RAN WG2 #68 “Carrier activation and de-activation” by GATT, Nov. 9-13, 2009); R2-096997 (3GPP TSG-RAN WG2 #68 “Discussions of CC configuration” by Fujitsu, Nov. 9-13, 2009); R2-096752 (3GPP TSG-RAN WG2 #68 “Activation and de-activation of component carriers” by Eriksson and ST-Eriksson, Nov. 9-13, 2009); and R2-095808 (3GPP TSG-RAN WG2 #67-bis “Activation and de-activation of component carriers” by Eriksson and ST-Eriksson, Oct. 12-16, 2009). There is also in UTRAN Release 8 a dual cell-HSPDA operation which in part includes a HS-SCCH order based activation/de-activation of a secondary downlink carrier was specified, and there is also a dual cell HSUPA operation in the UTRAN Release 9. See for example 3GPP TS 25.212 and 25.214.